1. Field of the Invention
The present invention relates generally to the brazing process, and more particularly to a method and apparatus for applying a coating of a solution that contains brazing alloy powders upon joints between different parts to be joined. The present invention may be used for a heat exchanger that includes an extruded metal tube and a corrugated fin which are joined together, and may also be applied to the manufacture of such heat exchanger. Furthermore, a coating head of a curtain coater apparatus comprises part of the present invention.
2. Description of the Prior Art
Typically, a conventional heat exchanger includes an extruded metal tube or pipe and a corrugated fin, which are joined together at the points where they engage each other, by means of a brazing process. In the conventional heat exchanger, the corrugated fin is formed from a brazing sheet that is clad with a sheet shaped brazing alloy and an aluminum sheet, and the respective portions of the tube and fin which engage each other are joined together by the brazing alloy component contained in the brazing sheet.
Recently, a brazing alloy powder solution was developed which contains a mixture composed of metal powders such as powdery aluminum (such as Al--Si alloy powders specifically used for the brazing process) and a binder, the mixture being obtained by mixing them together in a particular solvent. When this brazing alloy powder solution is used, it may be possible to obtain the corrugated fin simply by forming an aluminum sheet alone, without using the brazing sheet. Despite this usefulness, there is practically no effective means for placing the brazing alloy powders into the joints where the extruded metal tube and corrugated fin engage each other.
Tools that may be used for coating the brazing alloy powder solution upon the parts to be joined include brushing, rolling, spraying, and the like. These tools are not useful when a uniform coating thickness and reliable or stable coating during the successive coating process are critical factors.
For this purpose, it may be possible to use what is called a curtain coating process in the relevant field, whereby the coating solution containing the brazing alloy powders is allowed to flow like a curtain stream across, and each individual object being processed, such as an extruded metal tube, travels successively on the conveyor passage through the curtain stream. If the brazing alloy powders such as aluminum powders have a large particle size and specific gravity, they will tend to precipitate and settle down as the coating process progresses. As a result, uniformity of the composition of the coating solution cannot be maintained. This conventional curtain coating process is not suitable when a uniform coating thickness must be formed successively on all the objects being processed.